As one of large-capacity storage batteries, a redox flow battery (hereinafter, may be referred to as an “RF battery”) is known, the redox flow battery performing charging and discharging by circulating electrolytes to a positive electrode and a negative electrode which are arranged with a membrane being interposed therebetween (refer to Patent Literature 1). Patent Literature 1 discloses a cell stack in which cell frames, positive electrodes, membranes (ion-exchange membranes), and negative electrodes are repeatedly stacked. A cell frame includes a frame body and a bipolar plate integrated with the frame body. In the cell stack, between the bipolar plates of adjacent cell frames, a positive electrode and a negative electrode are arranged with a membrane therebetween, thus constituting a cell.